*WARNING: HYPOTHETICAL SCENARIO, POST WITH CARE*
Now before you go," Shepard ya retard," lemme explain. Since ME1&2 have both been out long enough for everyone to play them, I can do this without spoilers. As we all know, in ME 2 there was/is a possibility that Shepard could die in the final mission. After the mission is over, and if Shepard dies, Joker (Normandy's pilot) reports in to the Illusive Man and becomes enacting CO. If you're going,"huh?" right now allow me to unconfuse you: in the military the highest ranks of a company are CO and XO below he CO. Should the CO be discharged from active duty due to injury, illness, emergency, or breaking the law, all power and rank is turned over to the XO and he is made acting-Commanding Officer. So in a sense, Joker is now in charge of the Normandy and the crew, if Shepard dies that is. So I'm left asking myself," is Joker going to be the leader in ME 3?" it's not impossible. In ME 2 we saw him run and fire an assault rifle with some upgrades he got from Cerberus, giving him an exoskeleton or more upgrades could turn him to an effective a fighter as Shepard was.
So I'm asking this: if Shepard dies in Mass Effect 2, who is the commander in ME 3?
The character would have to match the following criteria in order to qualify for Shepard's job:
1) They must have appeared in each Mass Effect game in the console series
2) They must have some type of leadership&combat experience
3) They can't be a new character, we won't let them retcon what happened in ME 1&2
4) They must have some renown or be famous in the galaxy
5) They must be a character we would actually like to play as and are comfortable with
With the rules now known, here are our choices:
Joker- Now acting CO of the Normandy and crew and capable pilot/fighter despite his Vrolik's syndrome. He was one of Shepard's oldest and closest friends and has been with him throughout the entire journey. He's determined as Hell to show how much better he is than everyone despite the Vrolik's
Anders- Shepard's former CO and now sits as representative for humanity on the galactic council. Having former leadership&direct combat experience, renowned as heroic and decorated soldier, Anders is second candidate after Shepard to lead the galaxy against the Reapers
Wrex- now leader of his Krogan clan and (maybe by this time) Tuchanka, Wrex has an army of zealous and bloodthirsty warriors ready for the war to end all wars. Wrex shows himself to be exactly what you expect of a Krogan, while also holding a somewhat superior behavior and intelligence to the average Krogan with his ideas of how to cope with the Krogan Genophage. Wrex is a zealous general, fighter, and leader, and devoted to what could be the war to end all wars.
Liara- Liara, now the Shadow Broker, is arguably the most powerful being in the galaxy. With credits, soldiers, ships, and weapons at her disposal against the Reapers. Liara is also known for being a respected archeologist and information dealer before accepting her new position. She is also determined to finish what her lost love started.(if you romanced her)
Williams/Kaidan- both are Alliance soldiers who witnessed the Repaer first hand and disappointed at Shepard when they heard who he was working for. But now that their best friend/love has died and the world about to end, they feel the call to duty to finish what their commander started.
Go ahead and vote 'n' post, I may add other candidates later on.
... imagine how epic & sad it could be... hell that cutscene alone could give you lots of incentive to play the game 
